Changes in Forest Structure and Species Composition during Secondary Forest Succession in the Bolivian Amazon
Marielos Peña-Claros
(Click for Abstract)(Resumen Haga Clic Aquí)
Succession and Microelevation Effects on Seedling Establishment of Calophyllum brasiliense Camb. (Clusiaceae) in an Amazonian River Meander Forest
Rachel T. King
(Click for Abstract)(Resumen Haga Clic Aquí)
Species-specific Seedling Responses to Hurricane Disturbance in a Puerto Rican Rain Forest
Lawrence R. Walker, D. Jean Lodge, Sandra M. Guzmán-Grajales, and Ned Fetcher
(Click for Abstract)(Resumen Haga Clic Aquí)
Foliar C:N Ratio of Ferns along an Andean Elevational Gradient
Caroline Wegner, Meike Wunderlich, Michael Kessler, and Marcus Schawe
(Click for Abstract)(Resumen Haga Clic Aquí)
Fruit Bats (Chiroptera: Pteropodidae) as Seed Dispersers and Pollinators in a Lowland Malaysian Rain Forest
Robert Hodgkison, Sharon T. Balding, Zubaid Akbar, and Thomas H. Kunz
(Click for Abstract)
Lizard Assemblages from Natural Cerrado Enclaves in Southwestern Amazonia: The Role of Stochastic Extinctions and Isolation
Alison Melissa Gainsbury and Guarino Rinaldi Colli
(Click for Abstract)(Resumen Haga Clic Aquí)
Influence of Edge Exposure on Tree Seedling Species Recruitment in Tropical Rain Forest Fragments
Julieta Benítez-Malvido and Miguel Martínez-Ramos
(Click for Abstract)(Resumen Haga Clic Aquí)
Capture Rates of Male Euglossine Bees across a Human Intervention Gradient, Chocó Region, Colombia
J. Tupac Otero and Juan Carlos Sandino
(Click for Abstract)(Resumen Haga Clic Aquí)
Effects of Species, Density, Patch-type and Season on Post-dispersal Seed Predation in a Puerto Rican Pasture
Randall Myster
(Click for Abstract)
Morphological Variation in Two Facultative Epiphytic Bromeliads Growing on the Floor of a Swamp Forest
Cecília A. de Freitas, Fabio R. Scarano, and David D. Biesboer
(Click for Abstract)
Consequences of Habitat Fragmentation on Age Structure and Life History in a Tortoise Population
César Aponte, Guillermo R. Barreto, and John Terborgh
(Click for Abstract)
Gregarious Oviposition and Clutch Size Adjustment by a Heliconius Butterfly
Robert D. Reed
(Click for Abstract)
Expedition to Kubunitu
T. C. Whitmore
(Click for Abstract)
2003 Honorary Fellows
2003 Alwyn Gentry Award
2003 Excellence Award
Thanks to Editors and Reviewers 2002-2003
Changes in Forest Structure and Species Composition during Secondary Forest Succession in the Bolivian Amazon
Marielos Peña-Claros (mpenaibif@hotmail.com)
Changes in forest structure and species diversity throughout secondary succession were studied using a chronosequence at two sites in the Bolivian Amazon. Secondary forests ranging in age from 2 to 40 years as well as mature forests were included, making a total of 14 stands. Fifty plants per forest layer (understory, subcanopy, and canopy), were sampled using the transect of variable area technique. Mean and maximum height, total stem density, basal area, and species number were calculated at the stand level. Species diversity was calculated for each stand and for each combination of forest layer and stand. A correspondence analysis was performed, and the relationship between relative abundance of the species and stand age was modeled using a set of hierarchical models. Canopy height and basal area increased with stand age, indicating that secondary forests rapidly attain a forest structure similar in many respects to mature forests. A total of 250 species were recorded of which ca 50 percent made up 87 percent of the sampled individuals. Species diversity increased with stand age and varied among the forest layers, with the lowest diversity in the canopy. The results of the correspondence analysis indicated that species composition varies with stand age, forest layer, and site. The species composition of mature forests recovered at different rates in the different forest layers, being the slowest in the canopy layer. Species showed different patterns of abundance in relation to stand age, supporting the current model of succession.
Se estudio, usando una cronosecuencia, los cambios en la estructura del bosque y en la diversidad de especies durante la sucesión secundaria en dos sitios de la Amazonía boliviana. Se incluyeron bosques secundarios con un rango de edad de 2 a 40 años, así como bosques maduros, para un total de 14 rodales. Se inventariaron 50 plantas por estrato del bosque (sotobosque, subdosel, y dosel), usando transectos con área variable. Se calculó a nivel de rodal la altura máxima y mínima, la densidad total, el área basal y el número de especies. La diversidad de especies fue calculada para cada rodal y para cada combinación de estrato del bosque y rodal. Se realizó un análisis de correspondencia, y se modeló la relación entre la abundancia relativa de las especies y la edad del rodal, usando un grupo de modelos jerárquicos. La altura del dosel y el área basal aumentan con la edad del rodal, indicando que los bosques secundarios recuperan rápidamente la estructura de un bosque maduro. Se encontró un total de 250 especies, de las cuales aproximadamente el 50 porciento representaron al 87 porciento de los individuos muestreados. La diversidad de especies aumentó con la edad del rodal y varió con el estrato del bosque, con la diversidad más baja en el dosel. Los resultados del análisis de correspondencia indican que la composición de especies varía con la edad del rodal, el estrato del bosque, y el sitio. La composición de especies del bosque maduro se recupera con diferente rapidez en los diferentes estratos del bosque, siendo la recuperación más lenta en el dosel. La relación entre la abundancia relativa de las especies y la edad del rodal varia entre las especies, lo que respalda el modelo de sucesión actual.
Succession and Microelevation Effects on Seedling Establishment of Calophyllum brasiliense Camb. (Clusiaceae) in an Amazonian River Meander Forest
Rachel T. King (rachel@bio.miami.edu)
I investigated the effects of successional stage and micro-elevation on seedling establishment of Calophyllum brasiliense (Clusiaceae), a common canopy tree of seasonally flooded lowland forest along the Manu River meander zone in southeastern Peru. To compare seedling establishment between microhabitat types, I planted C. brasiliense seeds in a fully crossed experimental design of three successional stages (early, mid, and mature) and two micro-elevations (levees and backwaters). Seedling establishment success in this study was affected by both successional stage and micro-elevation, but micro-elevation was most important in mid-successional habitats. In general, seedlings in early succession experienced better conditions than in mature forest; light levels were higher, herbivory lower, and seedling growth higher. In mid-successional forest, micro-elevation determined habitat quality; backwaters had higher light levels, lower herbivory, and higher seedling growth and survival than levees. Mid-successional backwaters were similar in quality to early successional forest for seedling establishment, while levees in that same successional stage were the poorest microhabitats for establishment. Although mid-successional backwaters are similar to early succession for seedling establishment, in the long run, seedlings that establish in mid-succession have a lower chance of reaching reproductive size before their habitat ages to mature forest than members of their cohort that established in early succession. I hypothesize that successful recruitment for C. brasiliense in the Manu River meander system requires dispersal to early successional habitat.
Yo investigé el efecto de microhábitats del sistema serpentino ribereño, los cuales se diferencian en estado sucesional y en microelevación, en el establecimiento de plántulas de Calophyllum brasiliense (Clusiaceae), un árbol común en bosques estacionalmente inundados alrededor de los meandros del Río Manú en Perú. Para comparar establecimiento de plántulas entre los microhábitats, sembré semillas de C. brasiliense en seis condiciones de microhábitat, combinando los efectos de tres estados sucesionales (bosque temprano, mediano, y maduro) y dos microelevaciones (lomos y depresiones). El establecimiento de plántulas en este estudio fue afectado por estado sucesional y por microelevación, pero microelevación fue más importante en sucesión mediana. En general, plántulas en sucesión temprana tenían mejores condiciones que plántulas de bosque maduro; niveles de luz más altos, menor herbivoría, y una mayor tasa de crecimiento. En sucesión mediana, microelevacion determinó calidad de hábitat; depresiones presentaron más luz, menos herbivoria, y mayor crecimiento y sobreviviencia de plántulas que los lomos. Depresiones en sucesión mediano fueran similares en calidad a sucesión temprano en cuanto al establecimiento de plántulas, mientras que lomos en este mismo estado sucesional fueron los peores microhábitats para establecimiento. A largo plazo, las plántulas establecidas en sucesión mediano tienen menos probabilidad de alcanzar el tamaño reproductivo (antes de que el hábitat llega a ser bosque maduro) que las plántulas de la misma edad, establecidas en sucesión temprana. El reclutamiento efectivo de C. brasiliense en el sistema serpentino del Río Manú probablamente requiere la dispersión al hábitat de sucesión temprana.
Species-specific Seedling Responses to Hurricane Disturbance in a Puerto Rican Rain Forest
Lawrence R. Walker (walker@unlv.nevada.edu) , D. Jean Lodge, Sandra M. Guzmán-Grajales, and Ned Fetcher
Seedling dynamics were followed in a Puerto Rican forest for 20 months following a severe hurricane to study the interactive effects of hurricane debris, nutrients, and light on seedling diversity, density, growth, and mortality. Three treatments (debris removal, an unaltered control with hurricane debris, and chemical fertilization added to hurricane debris) altered levels of forest debris and soil nutrients. Canopy openness was measured twice using hemispherical photographs of the canopy. We examined the demographic responses of six common species to treatments over time. Seedling densities increased for all six species but the only significant treatment effects were increased densities of the pioneer tree Cecropia and the shrub Palicourea in the debris removal treatment. Seedling growth declined with declining light levels for four species but not for the pioneer tree Alchornea or the non-pioneer tree Dacryodes. Only Cecropia and the non-pioneer tree Chionanthus had treatment effects on growth. Mortality also differed among species and tended to be highest in the fertilized plots for all but Cecropia and Dacryodes. We found only some of the expected differences between pioneer and non-pioneer plants, as each species had a unique response to the patchy distributions of organic debris, nutrients, and light following the hurricane. High local species diversity was maintained through the individualistic responses of seedlings after a disturbance.
Seguimos la dinámica de plántulas en un bosque en Puerto Rico durante 20 meses después del huracán Hugo para estudiar el efecto de la interacción de hojarasca de huracán, nutrientes, y luz sobre la diversidad de especies, la densidad, el crecimiento, y la mortalidad. Establecimos tres tratamientos (remoción de hojarasca, control con la hojarasca de huracán inalterada, y fertilizante químico añadido a la hojarasca del huracán) para alterar los niveles de hojarasca en el bosque y los nutrientes en el suelo. Medimos luz directa e indirecta dos veces usando fotografías hemisféricas del dosel. La diversidad y la uniformidad en la distribución de especies pero no la riqueza de especies fueron reducidas en presencia de fertilización. Durante el estudio examinamos respuestas demográficas de seis especies communes a los tratamientos. La densidad de plántulas aumentó para todas las seis especies pero el único effecto de tratamiento fue el aumento en la densidad del árbol pionero Cecropia y el arbusto Palicourea en el tratamiento de remoción de hojarasca. El crecimiento de plántulas disminuyó según los niveles de luz disminuyeron para cuatro de las especies pero no para el árbol pionero Alchornea o el árbol no-pionero Dacryodes. Sólo el crecimiento de Cecropia y del árbol no-pionero Chionanthus fue affectado por los tratamientos. La mortalidad fue diferente entre las especies y tuvo una tendencia a ser mayor en las parcelas fertilizadas. Sólo encontramos algunas de las diferencias esperadas entre plantas pionera y no-pioneras. Cada especie respondió de forma única a la distribución en parches de hojarasca, nutrientes, y luz luego del huracán. La alta diversidad local de especies se mantuvo a través de las respuestas individualizadas de las plántulas después de la perturbación.
Foliar C:N Ratio of Ferns along an Andean Elevational Gradient
Caroline Wegner, Meike Wunderlich, Michael Kessler (106606.464@compuserve.com), and Marcus Schawe
We studied the concentration of leaf N and C among 183 fern species along an elevational gradient at 1700 to 3400 m in humid montane forest in the Bolivian Andes at different levels of taxonomic resolution. For two species of Elaphoglossum sampled 8 and 14 times, respectively, there were no elevational trends. Similarly, a contrast of 22 species with wide elevational amplitudes sampled at their highest and lowest locations did not show any change in C or N contents, or in C:N ratios with elevation. At the community level, however, the mean values of C:N ratios for (a) all species found at a given elevation showed a significant decline with increasing elevation and (b) among epiphytic species, higher ratios (i.e., lower relative N content) than among terrestrial species at the same elevation. These trends were opposite to those of the upper soil layer, in which C:N ratios increased with elevation.
Estudiamos la concentración de N y C en las hojas de 183 especies de helechos a lo largo de un gradiente elevacional a 1700-3400 m en bosque montane húmedo en los Andes bolivianos, a diferentes niveles de resolución taxonómica. Para dos especies de Elaphoglossum analizadas 8 y 14 veces, respectivamente, no encontramos cambios elevacionales. De mismo modo, una comparación de las localidades más bajas y altas de 22 especies con amplios rangos elevacionales tampoco mostró cambios en las concentraciones de C y N, o en la relación C:N. Al nivel de comunidades, sin embargo, el valor medio de la relación C:N ratios de (a) todas las epecies encontradas a una elevación dada disminuyó significativamente con la elevación, mientras que (b) epífitas mostraron valores más altos (es decir, concentraciones relativamente menores) que las especies terrestres en la misma elevación. Estas tendencias fueron opuestas a las de los valores del suelo, donde los valores de C:N incrementaron con la elevación.
Fruit Bats (Chiroptera: Pteropodidae) as Seed Dispersers and Pollinators in a Lowland Malaysian Rain Forest
Robert Hodgkison (rhodgkison@hotmail.com), Sharon T. Balding, Zubaid Akbar, and Thomas H. Kunz
The aims of this study were to (1) characterize the food resources exploited by fruit bats (Pteropodidae) within an old-growth Malaysian dipterocarp forest, (2) test the viability of the seeds they disperse, and (3) provide an estimate of the proportion of trees that are to some degree dependent upon bats for seed dispersal and/or pollination. Fruit species exploited by bats could be distinguished from those eaten by birds largely on the basis of color (as perceived by human beings). Bat-dispersed fruits were typically inconspicuous shades of green-yellow or dull red-brown, whereas fruits eaten by birds were generally bright orange to red. Dietary overlap between bats and nonflying mammals was relatively high. In contrast to primates and squirrels, which were major seed predators for several of the plant species under investigation, fruit bats had no negative impact on seed viability. A botanical survey in 1 ha of old-growth forest revealed that 13.7 percent of trees (>=15 cm girth at breast height) were at least partially dependent upon fruit bats for pollination and/or seed dispersal.
Lizard Assemblages from Natural Cerrado Enclaves in Southwestern Amazonia: The Role of Stochastic Extinctions and Isolation
Alison Melissa Gainsbury and Guarino Rinaldi Colli (grcolli@unb.br)
We used null model analyses to investigate the existence of structure in lizard assemblages from open vegetation enclaves in Rondônia, southwestern Amazonia, in relation to species richness, species co-occurrence, diet, and size overlap. These enclaves presumably have been isolated since the Holocene, providing a history of long-term isolation. We assumed that the presence of structure in lizard assemblages from the Rondônia enclaves is consistent with the notion that extinctions are a deterministic process, some species being more prone to extinction than others. We grouped enclaves into four categories: latosoil cerrado, sandy cerrado, transitional forest, and rocky field. We collected 14 Cerrado lizard species, consisting of five families in all sampled areas. Analyses of species richness, co-occurrence, diet overlap, and size overlap patterns suggested lack of organization in the assemblages. The assemblages from the rocky fields of Guajará-Mirim and the sandy cerrados in Vilhena were significantly structured in diet overlap, whereas the remaining assemblages lacked structure. This probably resulted from phylogenetic inertia and not from ecological interactions. Our results suggest that extinctions proceeded in a stochastic fashion and that historical factors had a dominant role in shaping lizard assemblages in detriment of present-day ecological factors. In addition, we identified endemic species in the enclaves as well as a tight association between unique ecogeographic features of the landscape and species occurrences. We propose that conservation measures in the region must adequately preserve these features to ensure the survival of the species.
Nós utilizamos análises de modelos nulos para investigar a existência de estrutura em taxocenoses de lagartos de enclaves de vegetação aberta em Rondônia, sudoeste da Amazônia, em relação riqueza de espécies, co-ocorrência de espécies, dieta e sobreposição de tamanho corporal. Esses enclaves presumivelmente estão isolados desde o Holoceno, proporcionando uma história de prolongado isolamento. Nós assumimos que a presença de estrutura nas taxocenoses de lagartos dos enclaves de Rondônia é consistente com a noção de que extinções são um processo determinístico, algumas espécies sendo mais sujeitas extinção do que outras. Nós agrupamos os enclaves em quatro categorias: cerrado sobre latossolo, cerrado sobre solo arenoso, floresta de transição e campo rupestre. Nós coletamos 14 espécies de lagartos do Cerrado, consistindo de cinco famílias em todas as áreas amostradas. As análises dos padrões de riqueza de espécies, co-ocorrência, sobreposição de dieta e sobreposição de tamanho do corpo sugeriram ausência de organização nas taxocenoses. As taxocenoses nos campos rupestres de Guajará-Mirim e cerrados arenosos de Vilhena foram significativamente estruturadas na sobreposição da dieta, enquanto que as taxocenoses restantes não foram estruturadas. Isso provavelmente resultou de inércia filogenética e não de interações ecológicas. Nossos resultados sugerem que as extinções ocorreram de maneira estocástica e que fatores históricos tiveram um papel dominante na formação das taxocenoses de lagartos, em detrimento de fatores ecológicos atuais. Ainda, nós identificamos espécies endêmicas nos enclaves, assim como uma forte associação entre feições ecogeográficas únicas da paisagem e a ocorrência de espécies. Nós propomos que medidas de conservação na região devem preservar adequadamente essas feições, para assegurar a sobrevivência das espécies.
Influence of Edge Exposure on Tree Seedling Species Recruitment in Tropical Rain Forest Fragments
Julieta Benítez-Malvido (jbenitez@oikos.unam.mx) and Miguel Martínez-Ramos
Edge creation has a pronounced influence on the understory vegetation, but the effects of edges on seedling species recruitment are still poorly understood. In Central Amazonia, 9-19 years after fragmentation, we recorded species richness and net seedling recruitment rate in 1 ha blocks exposed to none, one, or multiple edges within forest fragments. One-hectare blocks were located in the center (no edge), the edge (one edge), the corners (two edges) of 10 and 100 ha fragments, and in a 1 ha fragment (four edges). In 1991, we counted all tree seedlings 5-100 cm tall found within permanent 1 m2 plots located within the 1 ha blocks. In May 1993, we manually removed all seedlings that were smaller than 1 m tall from the permanent plots. Six years and five months later (October 1999), all new seedlings recruited into the plots were counted and classified into distinct morphospecies. Species richness of recruited seedlings, scaled by total seedling density, declined from the center to the edge, the corner blocks, and then to the 1 ha fragment. Overall, the four-edged, 1 ha fragment had the poorest species richness and the non-edged 100 ha central block the highest. The total number of recruited individuals was 40 percent less than that previously present, with the 100 ha corner having the lowest recruitment. Pairwise comparisons showed that species similarity was related to edge number for the 100 and 1 ha fragments. Species rank/abundance curves showed that a subset of species was common in all blocks within the fragments, and that the 100 ha center held more rare species than any other 1 ha block. This study demonstrated that, in a given fragment patch, the number of tree seedling species recruited varied inversely with the number of edges.
A formação de bordas influencia drasticamente a vegetação de sub-bosque, mas os efeitos sobre o recrutamento de espécies de plântulas ainda são poucos conhecidos. A riqueza de espécies e a taxa de recrutamento de plântulas na Amazônia Central em um período de 9-19 anos depois da fragmentação foram quantificadas em parcelas de 1 ha expostas a uma, nenhuma e várias bordas dos fragmentos. Estas parcelas de 1 ha foram distribuídas no centro (sem borda), na borda (uma borda), na esquina (dois bordas) de fragmentos de 10 e 100 ha e em um fragmento de 1 ha (quatro bordas). Em 1991, contamos todas as plântulas de espécies arbóreas, de 5 a 100 cm de altura dentro das parcelas permanentes de 1 m2. Seis anos e cinco meses depois (1999) todas as plântulas novas recrutadas foram contadas e classificadas em morfoespécies. A riqueza de espécies de plântulas recrutadas foi maior no centro, seguida de bordas e depois de parcelas de esquina de fragmentos de 10 e 100 ha. O fragmento de 1 ha apresentou a menor riqueza de espécies e a parcela central de 100 ha a maior. O número total de indivíduos recrutados foi 40% menor que o quantificado anteriormente e o menor recrutamento foi observado na esquina do fragmento de 100 ha. Comparações pareadas evidenciaram que a similaridade de espécies se relaciona com o número de bordas para os fragmentos de 100 e 1 ha. As curvas de amplitude/abundância de espécies demonstrou que determinado grupo de espécies era comum em todas as parcelas de todos os fragmentos, sendo que o centro do fragmento de 100 ha apresentou, comparativamente, mais espécies raras. Este estudo demonstrou que quanto maior o número de bordas em um fragmento, menor o número de espécies de plântulas arbóreas recrutadas.
Capture Rates of Male Euglossine Bees across a Human Intervention Gradient, Chocó Region, Colombia
J. Tupac Otero (Tupac.Otero@csiro.au), and Juan Carlos Sandino
Euglossine bees are important pollinators of lowland Neotropical forests. Compared to disturbed habitats, undisturbed ones have been previously characterized by higher abundance and diversity of euglossine bees. Most past studies have relied on chemically baiting male bees at single sites within habitats. Over a two-year period, we employed a repeated-measures design in which we sampled bees at multiple sites within three different habitat types, reflecting a mosaic of human disturbance (farm, secondary forest, and old logged forest). After 22 monthly samples, a total of 2008 male bees were captured, representing 31 species in five genera: 1156 at the farm (57.6%, 21 spp.), 505 in the secondary forest (25.1%, 27 spp.), and 347 in the old logged forest (17.2%, 21 spp.). Eighty-one percent of the bees captured belonged to the five most abundant species: Eulaema cingulata, El. chocoana, Euglossa hansoni, Eg. ignita, and Eg. imperialis. These species differed significantly in capture frequencies among habitats. Eulaema cingulata, El. chocoana, and Eg. ignita were captured most frequently at the farm, while Eg. imperialis was most abundant in the secondary forest. In contrast, Eg. hansoni, the sole short-tongued species among the five, was equally abundant in the two forest habitats but occurred rarely on the farm. Additionally, habitats differed in bee composition. The high capture rates for long-proboscis species at the farm may have been due to their ability to extract nectar from flowers with long floral tubes, which probably occurred at a greater density on the farmed land than in the adjacent forests.
Las abejas euglosinas son polinizadores importantes en bosques neotropicales de tierras bajas. Normalmente, los hábitats poco perturbados se caracterizan por presentar una mayor abundancia de abejas euglosinas que los menos intervenidos, aunque dichos resultados se basan en muestreos que usan atrayentes químicos para machos en sitios únicos por hábitat. En este estudio realizamos muestreos basados en sitios múltiples en tres hábitats adyacentes (finca, bosque secundario, y bosque maduro) a lo largo de dos años. Encontramos una mayor abundancia y diversidad de machos euglosinos en los hábitats con mayor perturbación humana que en el bosque maduro. Después de 22 muestreos mensuales capturamos un total de 2008 abejas representando 31 especies en cinco géneros: 1156 en la finca (57.6%, 21 spp), 505 en el bosque secundario (25.1%, 27 spp), y 347 en el bosque maduro (17.2%, 21 spp). El 80.8 por ciento de las abejas capturadas pertenecían a las cinco especies más abundantes: Eulaema cingulata, El. chocoana, Euglossa hansoni, Eg. ignita, y Eg. imperialis. Para estas especies encontramos diferencias en la frecuencia de captura entre hábitats. Eulaema cingulata, El. chocoana, y Eg. ignita fueron más frecuentes en la finca, mientras que Eg. hansoni, la única de las cinco con lengua corta, lo fue en los dos hábitats boscosos y Eg. imperialis en el bosque secundario. Adicionalmente, los hábitats difirieron en composición de abejas. Lo resultados pueden deberse a que en la finca había una mayor oferta de néctar con acceso restringido que en los busques adyacentes. El néctar, por estar en flores de corolas profundas, solo podía ser accedido por abejas de lenguas largas lo cual favorecía una mayor abundancia de euglosinas grandes con lenguas largas en la finca que en los bosques adyacentes.
Effects of Species, Density, Patch-type and Season on Post-dispersal Seed Predation in a Puerto Rican Pasture
Randall Myster (RMyster@ucok.edu)
An experimental study of seed removal of four woody species in an abandoned pasture revealed significant main effects of species, density (higher densities survived more than lower densities), and patch-type (seeds under shrub patches survived more than in grass patches), but no effects of season. Rates of seed loss decreased with seed size across species. Significant interactions between species and density and between species and patch-type were also observed.
Morphological Variation in Two Facultative Epiphytic Bromeliads Growing on the Floor of a Swamp Forest
Cecília A. de Freitas, Fabio R. Scarano (fscarano@biologia.ufrj.br), and David D. Biesboer
The epiphytic tank bromeliads Nidularium procerum (a CAM plant) and N. innocentii (a C3 plant) can be found as terrestrial plants in the understory of a Brazilian swamp forest. They occur in segregated patches differing in light and flooding regimes; however, plants of each species are found in the other species preferred habitat in a narrow boundary zone where the two populations meet. Although ecophysiological factors were previously thought to dictate the distribution of these species at this site, we suggest that their current distribution is probably related to colonization history and subsequent competition for space.
Consequences of Habitat Fragmentation on Age Structure and Life History in a Tortoise Population
César Aponte, Guillermo R. Barreto (guibarre@usb.ve), and John Terborgh
We studied changes in a population of red-footed Amazonian tortoises, Geochelone carbonaria, consequent to isolation in an insular forest fragment. Altered age structure, population density, and body growth rate are shown here for the first time to be associated responses. Age structure was strongly biased toward juveniles and growth rates were reduced compared to the mainland. Our data suggest that density-dependent processes induced by habitat fragmentation changed demography and life history parameters in a scant 16 years.
Gregarious Oviposition and Clutch Size Adjustment by a Heliconius Butterfly
Robert D. Reed (reed@u.arizona.edu)
Female Heliconius hewitsoni butterflies were found to aggregate during oviposition, producing multi-parent egg clutches. This behavior occurred when host plants were locally plentiful, indicating that females chose to oviposit gregariously. Collective clutch size correlated with host growth rate and with the number of females contributing to a clutch. Eggs did not positively bias host plant growth. Collective clutch size adjustment may represent a mechanism for facilitating larval "selfish herd" defense while reducing intraspecific competition.
Expedition to Kubunitu
T. C. Whitmore
This is a personal account of a 1964 expedition in search of two conifer species on Mts. Sasari and Kubunitu, the two highest peaks on Santa Ysabel in the Solomon Islands. Dacrydium xanthandrum and Dillenia crenata were both discovered in flower and collections were made. The account was recently discovered in Tim Whitmore's files.